As used herein, the terms “user equipment” and “UE” can refer to wireless devices such as mobile telephones, personal digital assistants, handheld or laptop computers, and similar devices that have telecommunications capabilities. Such a UE might consist of a wireless device and its associated Universal Integrated Circuit Card (UICC) that includes a Subscriber Identity Module (SIM) application, a Universal Subscriber Identity Module (USIM) application, or a Removable User Identity Module (R-UIM) application or might consist of the device itself without such a card. The term “UE” may also refer to devices that have similar wireless capabilities but that are not transportable, such as desktop computers, set-top boxes, or network appliances. The term “UE” can also refer to any hardware or software component that can terminate a communication session for a user. Also, the terms “user equipment,” “UE,” “user agent,” “UA,” “user device” and “user node” might be used synonymously herein.
As telecommunications technology has evolved, more advanced network access equipment has been introduced that can provide services that were not possible previously. This network access equipment might include systems and devices that are improvements of the equivalent equipment in a traditional wireless telecommunications system. Such advanced or next generation equipment may be included in evolving wireless communications standards, such as Long Term Evolution (LTE) and LTE-Advanced (LTE-A). For example, an LTE or LTE-A system might include an Evolved Universal Terrestrial Radio Access Network (E-UTRAN) node B (eNB), a wireless access point, or a similar component rather than a traditional base station. As used herein, the terms “eNB” or “access node” will refer to any component of a wireless network, such as a traditional base station, a wireless access point, or an LTE or LTE-A eNB, that creates a geographical area of reception and transmission coverage allowing a UE or a relay node to access other components in a telecommunications system. An access node may comprise a plurality of hardware and software. The term “legacy” may be used herein to refer to hardware, software, and standards related to LTE versions prior to LTE-A Release 10.
A traditional high power access node can create a relatively large area of coverage that can be referred to as a macro cell. Several different types of low power access nodes have been introduced that have a smaller area of coverage than a macro cell and that might improve the quality and reliability of the coverage provided by a macro cell. These low power access nodes include remote radio heads, pico eNBs, home eNBs (HeNBs), relay nodes, and similar components. These terms might be used interchangeably herein, or any such access node might be referred to generically as a low power node. An access node that creates a macro cell might be referred to herein as a macro eNB. The area of coverage created by a low power node might be referred to as a micro cell, a pico cell, a femto cell, a hotzone cell, a relay cell, a low power cell, or a similar term, any of which might be used interchangeably herein. Also, when a reference is made herein to an action being taken by a macro cell or by a low power cell, it should be understood that the action might be taken by the access node associated with that cell.
One difference between low power nodes and macro eNBs is a different propagation environment. In particular, low power nodes might be deployed indoors and might have different antenna heights and antenna patterns compared with macro eNBs. Also, the transmit power might be different for macro eNBs and low power nodes. For example, the maximum allowable transmit powers of a macro eNB, a remote radio head/pico, a HeNB, an outdoor relay, and an indoor relay are typically 46 dBm, 30 dBm, 20 dBm, 30 to 37 dBm, and 20 dBm, respectively, for a 10 MHz carrier bandwidth.
Heterogeneous networks are one of the important features in LTE-A. Heterogeneous networks consist of deployments where low power nodes are placed throughout a macro cell layout. As described below, a UE in a heterogeneous network might obtain higher quality, more reliable, or less costly service by attaching to a low power node rather than a macro eNB.